With decreasing feature sizes in semiconductor technology, it is obvious that effects due to crosstalk, in particular delay effects, can have a significant impact on the operation of an electronic device. Several commercially available tools for electronic design automation are now capable of calculating the delay effects of crosstalk. These tools operate on the basis of a gate-level description and can therefore not provide the required accuracy for giving a reliable estimate of the effects of crosstalk. Hence, it is desirable to calculate the effects of crosstalk on the basis of a transistor-level description, taking into account the non-linear behaviour of the transistors, so as to be able to verify the results provided by tools which are based on a gate-level representation of the electronic device.
When discussing crosstalk effects on the basis of a transistor-level representation of an electronic device, one may generally consider a situation as depicted in FIG. 7. FIG. 7 shows two RC-nets which will in the following be referred to as victim net 10 and aggressor net 20. These RC-nets generally consist of resistors 6 and capacitors 8, 9. In particular, the aggressor net 20 is coupled to the victim net 10 via a coupling capacitor 8. Further, both the victim net 10 and the aggressor net 20 are coupled to ground via a coupling capacitor 9. Input signals, in FIG. 7 schematically shown at 12 and 22, are supplied to the victim net 10 and the aggressor net 20 via driver stages 4. Similarly, an output signal at the output of the victim net 10 and the aggressor net 20 is received by an output side driver stage 4, which represents an output load to the victim net 10 and the aggressor net 20.
The signal situation is illustrated in FIGS. 8(a) and (b). Here one can distinguish between two different situations in which crosstalk has an effect on the response behaviour observe at an output of the victim net, i.e. at the output of the output side driver stage 4.
The first situation is illustrated in FIG. 8(a) and corresponds to the case that a signal transition is applied both to the input side driver stage 4 of the victim net 10 and to the input side driver stage 4 of the aggressor net 20. In FIG. 8(a) the input signal of the aggressor net 20 is shown as a function of time and denoted by A. The output signal of the victim net, taking into account the effects of crosstalk, is denoted by V. For comparison, the output signal of the victim net 10 is shown as a dashed line denoted by V′. As can be seen, the output signal V of the victim net is significantly affected by the signal transition applied to the aggressor net 20.
Two effects can be seen from the illustration of FIG. 8(a): Firstly, the rising edge of the output signal V of the victim net 10 is shifted to a later time as compared to the behaviour of the output signal V′ without the influence of crosstalk. This crosstalk-induced delay is in FIG. 8(a) denoted by Δt. Secondly, the slope of the rising edge of the output signal V of the victim net 10 is modified. In particular, the transition time, which may be defined as the difference in time between a first time t1, at which the output signal V has increased to 20% of the total amplitude Δx of the output signal V, and a second time t2, at which the output signal V has increased to 80% of the total amplitude Δx, is significantly larger as compared to the situation without crosstalk.
In FIG. 8(a) there is also shown a situation in which the signal transition of the aggressor net is directed into the same direction as the signal transition of the victim net 10. This is illustrated by dotted lines denoted by A′ and V″. Here, the effect of crosstalk is to shift the signal transition observed at the output of the victim net 10 to an earlier point of time.
A second situation is illustrated in FIG. 8(b). This situation corresponds to the case in which no signal transition is present on the victim net 10. Again, the input signal of the aggressor net 20 is denoted by A, the output signal of the victim net 10 is denoted by V, and the output signal of the victim net 10 neglecting the influence of crosstalk is denoted by V′. As can be seen from the dashed line, the output signal V′ without the influence of crosstalk remains at a constant value, while a bump occurs in the output signal V which is due to the capacitive coupling between the victim net 10 and the aggressor net 20. The maximum deviation of the output signal V from the behaviour of the output signal V′ without crosstalk is in FIG. 8(b) denoted by xn and represents the amplitude of noise induced by crosstalk. Of course, instead of using the amplitude xn of the crosstalk-induced noise, the crosstalk-induced noise may also be quantified in terms of a signal power or in terms of the area enclosed between the trajectories of the output signal V with crosstalk and the output signal V′ without crosstalk.
For electronic circuit designs with practical relevance the situation is, however, more complex. FIG. 9 illustrates a signal path of an electronic device which consists of a sequence of RC-nets connecting a path start point 110 with a path end point 120. The RC-nets are connected one after the other via driver structures 4. Each of the RC-nets forms a victim net 10 which is capacitively coupled to at least one aggressor net 20. As in FIG. 8, the victim nets 10 and the aggressor nets 20 are also capacitively coupled to ground. When running simulations of such a full signal path 100 on a transistor level the effects of all the aggressor nets would have to be considered simultaneously for each victim net 10 of the signal path 100. This is entrained by a very long run time of the simulation and renders this approach impracticable for signal paths in typical electronic circuit designs. Moreover, each of the aggressor nets 20 typically has connected to its input side driver structure 4 a more or less complicated logic circuit structure, which further complicates the simulation.
Therefore, accurate and efficient simulations of the effects of crosstalk, which are based on a transistor-level model description, e.g. using SPICE or HSPICE, have not been practicable.